In this study, we aimed to examine health-related quality of life during the COVID-19 pandemic among a general sample of young people in Norway aged 11–19 years. More specifically, we examine: (1) Change over 2 time-points in five health-related quality of life dimensions, (2) Whether sociodemographic- and COVID-19-related factors contributed to change in these five dimensions, (3) Whether parental stress and socioeconomic status at T1 interacted with change in health-related quality of life across T1 and T2. Data collection lasted from April 27th to May 11th, 2020 (T1), and from December 16th, 2020, to January 10th, 2021 (T2). Youth aged 11–19 years (N = 2997) completed the KIDSCREEN-27, COVID-19 related and sociodemographic items. Parents (N = 744) of youth aged 15 years and younger completed the parental stress scale and sociodemographic items. Physical and psychological wellbeing declined significantly from March to December 2020. Subscale scores for social support and peers increased. Controlling for a broad number of sociodemographic and COVID-19-related factors did not make an overall impact on the estimates. Those worried about infection, older aged, girls, and youth born outside Norway had a steeper decline in health-related quality of life subdimensions from T1 to T2. In the wake of the COVID-19 pandemic, we warrant special attention to the recovery of youth's physical and psychological wellbeing.